1. Field of the Invention
This invention relates to apparatus for controlling the filling of a container by ultrasonic sound waves. More particularly, the invention relates to new and improved methods and apparatus for providing a cut-off signal for closing a fill valve when the level of liquid material or the like being delivered to a container has reached a predetermined level in the container can.
2. Description of the Prior Art
Ultrasonic pulse echo ranging systems for monitoring the depth of liquid in tanks are known. In one such system, a transducer, located in the bottom of the tank, directs pulsed energy upwardly. The depth of liquid is determined by measuring the time required for the ultrasonic energy to be transmitted to and then reflected by the surface of the liquid in the tank.
In another system, the level of sludge in a reservoir is measured by transmitting 80 microsecond pulses of ultrasonic energy at 200 kHz every 11/2 seconds from a point beneath the surface of the fluid in a reservoir adjacent the bottom. To exclude response to stray particulate matter suspended in the liquid above the level of the sludge, this system utilizes four consecutive outputs of the echo signal to trigger a control signal.
In still another system, a variable width gate provides a time "window" during which a pulse system is gated open to receive an echo pulse in an ultrasonic system for measuring the distance from a transducer to both the surface of a liquid and the bottom of a channel through which the liquid is flowing.
While the above prior art systems are generally effective for measuring liquid level in large bodies of fluid having substantial sonic travel times, attempts to use them for measuring liquid levels in containers over a short distance have generally been ineffective due to insufficient short range capability and the inability to resolve the small distances needed for accurate filling as well as due to inability to withstand ambient noise conditions. Thus, it is necessary for the measuring ultrasonic beam from the transducer to enter the mouth of the can alongside of the fill spout. Sound reflected from the liquid surface inside of the can must then travel back to the transducer. The sound waves can be interfered with by foaming of the liquid on the surface when filling is done at a high rate. In addition, false echoes from the bottom of the can can produce false readings which can result in premature shut-down of the filling operation.
It is known in the art of filling systems to use a light beam transmitted at an angle to the surface of the liquid. When the beam was reflected from a surface at the desired level, it impinges on a photocell and generates a control signal. This system may be adversely affected by the reflecting property of the material being filled such as with dark paints and transparent varnishes.
It is an object of the present invention to provide an apparatus utilizing ultrasonic energy for accurately determining the level of a fluid in containers as small as 1/4 pint in capacity and even smaller as the container is filled at a high rate, and for providing controlled shut-off of the flow of liquid into the container.
It is another object of the invention to use echo ranging of ultrasonic energy to control a filling operation.
It is also an object of the invention to measure a liquid level in a container during a filling operation by the use of pulsed ultrasonic energy.
It is a further object of the invention to provide a plurality of echo ranging measurements of ultrasonic energy reflected by a liquid level during a filling operation.